1. Field of the Invention
The present invention relates to a crank axle unit mounted in a bottom bracket assembled to a bicycle frame, and to the technique of positioning and fixing this unit to the bottom bracket. In particular, the invention relates to a crank axle unit comprising a tubular element surrounding and rotatably supporting a crank axle, and a fixing device for positioning and fixing the tubular element in the bottom bracket.
2. Description of the Related Art
A crank axle unit as noted above is disclosed in Japanese Utility Model Publication Kokai No. 1989-180393, for example. This crank axle unit includes a first screw ring for fitting to an outside wall of one end region of a tubular element and screwing to an inside wall of one end region of a bottom bracket, and a second screw ring for fitting to an outside wall of the other end region of the tubular element and screwing to an inside wall of the other end region of the bottom bracket. The two screw rings have grooves defined on outer peripheries thereof to act as engaging portions engageable with a screwing tool. That is, the screw rings are turned by a tool acting on the outer peripheries thereof.
According to this construction, these engaging portions have extended axial lengths to allow the screw rings to be turned until the screw rings are screwed into the bottom bracket to extents corresponding to predetermined lengths for assembly purposes, and to prevent deformation of the engaging portions of the screw rings due to the reaction to turning and tightening of the screw rings to the limits. Consequently, the screw rings project to relatively large extents from the bottom brackets when the screw rings are assembled to the bottom bracket as designed. Front gears and cranks must therefore be located at relatively remote positions laterally of the bottom bracket to be out of contact with the screw rings.